1. Field of the Invention
This invention relates to a position pointer suitable for use for detection of writing pressure, a variable capacitor for detecting the writing pressure, and an inputting apparatus which includes the position pointer.
2. Description of the Related Art
In recent years, inputting apparatuses have been used as an inputting device for computing devices, such as personal computers and so forth. A typical inputting apparatus includes a position pointer formed, for example, like a pen, and a position detection apparatus having an input face which receives a pointing operation or inputting of characters, figures, and so forth thereto using the position pointer.
A variable capacitor as disclosed, for example, in Japanese Patent Laid-Open No. Hei 4-96212 (hereinafter referred to as Patent Document 1), is used in a writing pressure detection section of the position pointer. The variable capacitor disclosed in Patent Document 1 includes a first electrode attached to a first face of a dielectric member and a second flexible electrode disposed on a second face side of the dielectric member. The variable capacitor further includes means for spacing the second electrode away from the second face of the dielectric member by a small distance, and means for applying relative pressure or displacement between the second electrode and the dielectric member.
FIGS. 41A and 41B show a particular configuration of the conventional variable capacitor. More particularly, FIG. 41A shows the variable capacitor in an initial state, and FIG. 41B shows the variable capacitor in another state wherein pressure is applied thereto.
Referring to FIGS. 41A and 41B, the variable capacitor 200 includes a dielectric member 201 substantially shaped as a disk, a first electrode 202 attached to the first face 201a of the dielectric member 201, and a second electrode 203 disposed on the other face 201b side of the dielectric member 201 opposite the first face 201a of the dielectric member 201. The second electrode 203 has flexibility and is disposed on the second face 201b side of the dielectric member 201 with a ring-shaped spacer 204 interposed therebetween. Meanwhile, a bar-like rod 210 is provided on the opposite side of the second electrode 203, opposite to the dielectric member 201, with an elastic member 205 interposed therebetween.
A first terminal 206 is provided on the first face side of the first electrode 202. The first terminal 206 has a disk-shaped flange portion 206a and a lead portion 206b extending from a substantially central portion of a face of the flange portion 206a. When writing pressure is applied to the flange portion 206a (through the rod 210), the flange portion 206a contacts the first face of the first electrode 202 and electrically connects to the first electrode 202.
A second terminal 207 is provided at an end portion of the second electrode 203. The second terminal 207 has, similarly to the first terminal 206, a disk-shaped flange portion 207a and a lead portion 207b extending from a substantially central portion of one face of the flange portion 207a. When writing pressure is applied to the flange portion 207a, the flange portion 207a is brought into contact with an end portion of a face of the second electrode 203 and electrically connects to the second electrode 203.
In the variable capacitor 200, in a state wherein no pressure or displacement is applied to the rod 210, that is, in an initial state, a small distance is formed between the second face 201b of the dielectric member 201 and the second electrode 203 by the spacer 204 as seen in FIG. 41A. On the other hand, if pressure is applied to the rod 210, then the elastic member 205 and the second electrode 203 are pressed and elastically deformed by the rod 210 as seen in FIG. 41B. By the elastic deformation, the second electrode 203 is brought into contact with the second face 201b of the dielectric member 201. Then, if the contact area between the second electrode 203 and the second face 201b of the dielectric member 201 increases, then the capacitance value between the first and second terminals 206 and 207 also increases. As a result, if the variation in capacitance value between the first and second terminals 206 and 207 is detected, then the writing pressure applied to the rod 210 is detected.